It tracks a nationwide index of long-term municipal bonds and holds roughly 600 high-quality municipal bonds with remaining maturities of 12 years or more. It is built from securities not subject to the federal alternative minimum tax, which preserves the purity of its tax benefits.

It suits investors in high income tax brackets who need to maximize after-tax returns, as well as those who expect interest rates to fall and want to capture price appreciation on long-term bonds.

It is a passively managed (index-tracking) ETF launched by BlackRock in 2023.

The fund selects US investment-grade municipal bonds with long remaining maturities and holds them on a market-capitalization-weighted basis. By keeping a high allocation to long-dated bonds, it aims to secure higher coupon rates and longer duration than typical municipal bond funds.

• A portfolio specialized in municipal bonds with maturities of 12 years or more
• Exemption from federal income tax and the alternative minimum tax

Assets under management (AUM) stand at $1.9B, and the expense ratio is 0.09% per year.

Unlike MUB, the flagship municipal bond product that spans all maturity ranges, LMUB concentrates only on long-dated bonds, so its price volatility in response to interest rate changes is considerably larger.

The fund reacts sensitively to long-term interest rate movements driven by inflation trends and shifts in monetary policy. As the recent high-rate environment has persisted, its after-tax appeal has tended to remain at a high level.

It is a product that consistently draws asset allocation demand from high-income, high-net-worth investors who want to lock in long-term tax-exempt income during periods when rates are perceived to be near a peak, while also pursuing the potential for price gains.

Its strengths are high after-tax interest income and strong price elasticity when rates fall, but investors should be cautious about the high interest rate risk that comes with long duration.

If you want lower volatility and broader municipal bond exposure, MUB, which covers the entire market, can be a sensible choice. If you are looking for Vanguard's low-cost long-term municipal bond product, VTEL is also a good alternative, and to maximize short-term tax benefits, you can also consider products such as SUB or TFI.

These are the key factors to weigh carefully before deciding to invest in LMUB. You need a deep understanding of both the distinctive tax benefits of long-term municipal bonds and the price volatility risk that comes with long maturities.

Investors should clearly recognize that in a phase of sharply rising market interest rates, principal losses large enough to far outweigh the tax exemption benefit can occur.

For aggressive bond investors who actively seek additional returns from future rate declines on top of stable tax-free income, it can be a highly efficient investment vehicle.